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The powder X-ray diffraction (PXRD) analysis and the electromotive force (emf) measurements have been used to investigate the Sb–Te–S system in the Sb2S3-Sb2Te3-Te-S composition region at 300–450 K temperatures interval. Relative partial molar functions of antimony in alloys have been calculated and obtained data have been used to get self-consistent sets of the standard Gibbs free energy, standard enthalpy, and standard entropy of the Sb2S3 and Sb2Te2S compounds, as well as the Sb2Te2,4S0,6 and Sb2Te2,7S0,3 solid solutions. The data obtained for Sb2S3 have been compared to the ones available in the literature. Thermodynamic functions of the Sb2Te2S compound, as well as, the Sb2Te2,4S0,6 and Sb2Te2,7S0,3 solid solutions have been determined for the first time.

The Bi–S–Te system has been studied using emf measurements in the composition region Bi2S3–Bi2Te3–Te–S at temperatures in the range 300–450 K. We have calculated relative partial molar functions of bismuth in alloys and used the results to obtain self-consistent sets of the standard Gibbs free energy, standard enthalpy, and standard entropy of the Bi2S3, Bi2Te3, and Bi2Te2S compounds and a solid solution with the composition Bi2Te1.8S1.2, based on the last compound. The data obtained for Bi2S3 and Bi2Te3 have been compared to data available in the literature. The thermodynamic functions of Bi2Te2S and Bi2Te1.8S1.2 have been determined for the first time. [ABSTRACT FROM AUTHOR]

Abstract In general, Bi 2 Te 3 and related alloys show the best thermoelectric performance at near-room temperature region below about 423 K, which is in some cases not high enough for waste heat recovery. In order to raise the operation temperature on the basis of Bi 2 Te 3 technology, S element was introduced into Bi 2 Te 3 to synthesize a ternary tetradymite compound, Bi 2 Te 2 S, and the thermoelectric properties were analyzed. In this study, Bi 2 S 3 was considered, instead of using elemental S, to avoid the issues arising from the volatility of S. Compared with Bi 2 Te 3 , undoped Bi 2 Te 2 S shows higher Seebeck coefficients (S max = −210.9 μV K−1 at 523 K) but also higher resistivity (ρ min = 26.5 μΩ m at 323 K), resulting in decreased power factor (PF max = 1.49 mW K−2m−1 at 373 K). However, low thermal conductivity (κ min = 0.987 WK−1m−1 at 473 K) produced higher ZT at T ≥ 423 K than Bi 2 Te 3 , reaching about 0.66 at 473 K. At the same time, the bipolar conduction was reduced due to the enlarged band gap of about 0.22 eV, which was estimated from the S - T curve. After additional hot deformation at 793 K, undoped Bi 2 Te 2 S shows remarkably improved values of power factor (PF max = 2.62 mW K−2m−1 at 323 K) and ZT (ZT max = 0.86 at 473 K), which was ascribed to increased carrier concentration. In addition, the highly anisotropic transport properties of Bi 2 Te 2 S were suggested to be another origin, which was revealed by the first-principles calculations. In summary, Bi 2 Te 2 S is a promising candidate for thermoelectric generation at the intermediate temperature region 473–573 K where Bi 2 Te 3 shows degraded performances. Highlights • Ternary tetradymite Bi 2 Te 2 S was sintered using Bi, Te, and Bi 2 S 3. • Hot deformation was additionally applied to improve the thermoelectric performance. • The maximum power factor increased from 1.49 to 2.62 mW m−1K−2 by hot deformation. • The maximum figure of merit of 0.86 was obtained from the hot-deformed Bi 2 Te 2 S. [ABSTRACT FROM AUTHOR]

Thermoelectric effects are one of the promising ways to utilize waste heat. Novel approaches have appeared in recent decades aiming to enhance thermoelectric conversion. The theory of energy filtering of free carriers by inclusions is among the latest developed methods. Although the basic idea is clear, experimental evidence of this phenomenon is rare. Based on this concept, we searched suitable systems with stable structures showing energy filtering. Here, we report on the anomalous behavior of Cr-doped single-crystal Bi 2 Se 3 that indicates energy filtering. The solubility of chromium in Bi 2 Se 3 was studied, which is the key parameter in the formation process of inclusions. We present recent results on the effect of Cr-doping on the transport coefficients on a wide set of single crystalline samples. Magnetic measurements were used to corroborate the conclusions drawn from the transport and X-ray measurements. [ABSTRACT FROM AUTHOR]

We report on the electrical and thermal transport properties of the Sn 1− x Pb x Bi 2 Te 4 series and we discuss the potential of these materials for thermoelectric conversion applications. From the evolution of the XRD patterns, we can confidently conclude that a complete solid solution exists between SnBi 2 Te 4 and PbBi 2 Te 4 , with no miscibility gap. A crossover from p-type conduction in Sn-rich samples to n-type conduction in Pb-rich ones has been observed, with a transition between x =0.3 and 0.4. A concomitant increase of the electrical resistivity and of the Seebeck coefficient has been observed in the solid solution, which leads to almost constant values of the thermoelectric power factor. Moreover, the thermal conductivity is slightly reduced in the solid solution. The best figure of merit ZT values at room temperature have been observed for p-type Sn 0.8 Pb 0.2 Bi 2 Te 4 with ZT =0.25 and for n-type Sn 0.3 Pb 0.7 Bi 2 Te 4 with ZT =0.15. [ABSTRACT FROM AUTHOR]

Bismuth tellurides (tetradymite and tellurobismuthite) were identified in the heavy mineral fraction of alluvial placers from Pukanský potok brook near Pukanec, Štiavnické vrchy Mountains, Slovak Republic. They forms only very slightly rounded aggregates up to 5 mm in size with typical perfect cleavage. Aggregates of bismuth tellurides from Pukanec are mostly represented by tetradymite, which has an uniform chemical composition and only minor contents of Se (up to 0.10 apfu) and Sb (0.01 apfu) were detected. Its empirical formula is (Bi2.00Sb0.01)Σ2.01Te1.99(S0.92Se0.08) Σ 1.00 on basis of 5 apfu. Tellurobismuthite was observed as microscopic oval or irregular elongated inclusions in tetradymite. Only rarely aggregates of tellurobismuthite up to 3 mm in size with thin tetradymite rim were observed. The chemical composition of tellurobismuthite is nearly close to the end member, it has only minor contents of Se (0.02 apfu) and Sb (0.02 apfu) and its empirical formula is (Bi2.01Sb0.02)Σ2.03(Te2.96Se0.01)Σ2.97 on basis of 5 apfu. This find of bismuth tellurides indicates the existence of previously unknown primary Bi-Te mineralization near Pukanec, but its connection to the epithermal Au-Ag mineralization is not clear. [ABSTRACT FROM AUTHOR]

Gold was one of ores of lower importance in the Březové Hory ore deposit, Příbram, Czech Republic. Although gold was relatively common in the Příbram area, specimens with macroscopic gold grains from the Březové Hory deposit were very rare. The studied sample was collected on dump of the Ševčin Mine in year 2003 and consists of milky grey quartz, pyrite, arsenopyrite with native gold and tetradymite. Gold forms up to 0.5 mm large aggregates growing in quartz and intergrowth with pyrite and tetradymite. The fineness of gold is 0.954, the silver content is about 0.079 apfu. Tetradymite is chemically homogenous with higher Sb content (0.028 - 0.050 apfu). [ABSTRACT FROM AUTHOR]